This is what I finally came up with - no real errorchecking tho =/ And man, I've used things I've never touched before.. and the redim preserve, that took like ages to acctually figure out how to do it.
Code:
If NOT @LOGONMODE
	Break On
EndIf

Dim $SO

$SO = SetOption("Explicit","On")
$SO = SetOption("NoVarsInStrings","On")
$SO = SetOption("NoMacrosInStrings","On")
;
dim $counter,$key,$val
dim $wr,$add,$wri
dim $split[],$c,$x
dim $sp[],$spl,$
;define values
$counter=0
$key='HKEY_CURRENT_USER\Software\Golfing'
$val='Round02'
$add='28,00,00,00,ff,ff,ff,ff,02,00,00,00,03,00,00,00,3c,00,00,00,50,\'+  '00,00,00,fe,ff,ff,ff,b2,03,00,00,02,05,00,00,02,04,00,00'
$wri='28000000ffffffff02000000030000003c00000050000000feffffffb203'+
'00000205000002040000'


$wr=readvalue($key,$val)
$split=split($add,',')


for each $c in $split
select 
case $counter = 2 $c = 'bc' Redim preserve $sp[$counter] $sp[$counter]=$c 
case 1 if instr($c,'\') $x=substr($c, len($c) - 1, 3) 
       $=trim($x) Redim preserve $sp[$counter] 
       $sp[$counter]=$x else Redim preserve $sp[$counter] $sp[$counter]=$c endif
endselect
$counter=$counter+1
next

ReDim $counter
$counter=0

for $counter = 0 to ubound($sp)
$spl = $spl + $sp[$counter]
next

/*
$wr ' Read value from reg' ?
$wri ' should be equal to line above'  ?
$spl ' this is what we wanna write' ?
*/
if $wr = $spl 'entry already altered' ? exit @error 
else 
$wr=writevalue($key,$val,$spl,'reg_binary') 
if @error 'error: ' + @ERROR @SERROR + ' ' ? 
else 
'altered key' ? endif endif


I just noticed that my fifth edit of this post has gone a-wall, and my final part that acctually did what it more or less was supposed to is gone..
Provided below:
Code:
If NOT @LOGONMODE
	Break On
EndIf

Dim $SO
Dim $wro[],$apa,$count,$counter,$wr,$wri,$key,$val,$to,$o,$
$SO = SetOption("Explicit","On")
$SO = SetOption("NoVarsInStrings","On")
$SO = SetOption("NoMacrosInStrings","On")
$key='HKEY_CURRENT_USER\Software\Golfing'
$val='Round02'
$count=0
$counter=0

$wri=readvalue($key,$val)

 for $count=0 to 80 step 2
  $o=right(ltrim(substr($wri, 1, $count)),2)
  if $count=6 $o='bc' endif
  ReDim preserve $wro[$counter] $wro[$counter]=$o 
  $counter=$counter+1
 next
ReDim $counter
$counter=0

 for $counter = 0 to ubound($wro)
  $to= $to + $wro[$counter]
 next 

 ;$to ?
 ;$wri ?
if $to = $wri 'entry already altered' ? exit @error 
else 
$wr=writevalue($key,$val,$to,'reg_binary') 
if @error 'error: ' + @ERROR @SERROR + ' ' ? 
else 
'altered key' ? endif endif

This still lacks errorchecking - and uses the wrong key-structure.., but should be the code-snippet that you could comment. Interesting that you didn't notice that it didn't do the job correctly